Slack (and SlackRTM) replyInThread() doesn't reply if message came from a thread

[drakenya]

• BotMan Version: 1.5.2
• PHP Version: 7.1.3
• Messaging Service(s): SlackRTM
• Cache Driver: none

Description:

The replyInThread() function grabs the message's 'ts' attribute and includes that in the payload it sends. This works for starting a new thread, but it fails for continuing an existing thread. If it tries to post to an existing thread, it just does nothing (sends to Slack, but ends up in oblivion).

It should check if thread_ts is set, and if so use that; otherwise, use ts. Something like this:

$additionalParameters['thread_ts'] = !empty($matchingMessage->getPayload()->get('thread_ts'))
            ? $matchingMessage->getPayload()->get('thread_ts')
            : $matchingMessage->getPayload()->get('ts');

This would be added in SlackRTMDriver->replyInThread() and SlackDriver->replyInThread()

Steps To Reproduce:

Have the bot listen for a message, and use SlackTRMDriver->replyInThread()

Send a message in the channel, and the bot replies in a new thread.

Reply with same message in the thread, and the bot never gets the message to post to that thread.